The first thing you should always do when you create a new world in Create-a-World (CaW), is to go here:
My Documents/Electronic Arts/The Sims 3 Create A World Tool/UserToolData/Worlds
You'll see three files that are related to your new world:
(1) a folder that uses the name you just gave your new world;
(2) a settings file for your new world; and
(3) your actual world file.
Open the folder. Inside, there are two other folders. Open the Layers folder. In there, you'll find a file that starts with GlobalLayer_, with a bunch of letters and numbers after that, before the .layer extension. Copy that file, and paste it into a folder that's in a safe place, and name the folder appropriately to tell you that's where you put a copy of the clean global layer for your new world.
You should also write down, somewhere, what height map you used to initiate your world. You'll need that information if you need to make a NEW clean global layer at any time.
If you didn't copy your clean global layer and save a copy somewhere when you made your new world, and you have been working on your world for a while, and if you have used Edit-in-Game (EiG), your global layer for your new world has probably gotten pretty cluttered. The files kept in there can mess up your world when it's exported and made into a .Sims3Pack file, so you should always have a clean global layer file to copy into your world's layers, just before you export.
Here's how to get a clean global layer if you didn't save one (as shown above) initially.
(1) Download the XVI32 Hex Editor here:
http://www.chmaas.handshake.de/delphi/f ... /xvi32.htm
Unzip it to a folder wherever you want. It doesn't need to be installed. You'll just be using the .exe file that's contained in the .zip.
(2) If you don't have S3PE, download it here:
http://www.den.simlogical.com/denforum/ ... opic=189.0
Install it, then open it. Using the Settings/External Programs tab, associate the XVI32 hex editor. Close S3PE.
(3) BACK UP THE WORLD THAT NEEDS A NEW GLOBAL LAYER--be sure to copy the folder, the settings, and the .world file to a safe place.
(4) Go into CaW and create a new world using the same height map you used with your other world (see why you needed to write that down?). Name the new world anything you want...Cleanup might be a good name. Close CaW.
NOTE: As you can see in that picture, I saved my new world as Cleanup-300SmallFlat, so that if I ever need to clean up a global layer for that same size world, I will already have a file I can use for the process.
(5) Go into S3PE and open your Cleanup world.
(6) Click on the column heading "Type," so that all of the 0x00... numbers come up first. Then scroll down and look for the file named 0x0498DA7E (It says UNKNOWN in the Tag column).
(7) Right-Click on that line, and from the pop-up menu, choose Hex Editor. When the editor opens up, write down the numbers that are in the grid. Remember...there are no capital letter Os...there are only zeros (0). That's important for when you have to re-use these numbers.
(8) Close the Hex Editor, then Close S3PE.
(9) Go to your Worlds folder and open the Cleanup world's folder, then open the Layers folder. You'll see ONLY the global layer file in there. COPY that.
(10) Go back to the Worlds folder and open your original worlds' folder, then open the Layers folder. DELETE the existing global layer file, then PASTE the file you just copied from the Cleanup world. Don't worry that the number at the end doesn't match the other layer numbers.
(11) That new global layer now needs to be associated with your original world. Open S3PE again, open your original world, and find the 0x0498DA73 line again. Open it in the Hex Editor. You'll see a different number there, than you saw before (because it's showing the number from the original world).
(12) Type the numbers you wrote down (the ones from the Cleanup world), over the numbers that show in the new grid. Using the Hex Editor's File menu, Save. Then quit the Hex Editor.
(13) S3PE will pop up a question asking if you want to commit to saving the new number. Click Yes.
(14) You'll now see two of the 0x0498DA73 lines. One is crossed out. The other one is your new one, which will be your new clean global layer.
(15) in the S3PE File menu, click Save, and once that's done, quit S3PE.
(16) Open CaW and open your original world (for which you just cleaned the global layer). When it's open, click on the global layer to open it. You'll find that it has nothing listed in it. Woot!
(17) Save the world and quit CaW.
(18) Backup all three parts of the world (the folder, the settings, and the .world file) to a safe place. Then also make a separate copy of the global layer file from the Layers folder (as I told how at the start of this tutorial).
After you've completed all this, you can continue to build your world as before. Just remember to check to see if your global layer is still clean, before you export to make a new .Sims3Pack file. If it's not clean, backup all of your CaW files for the world, then delete the existing global layer from the Layers folder, then copy your clean global layer and paste it into the Layers folder. Then export your world.